The fruit has distinctive ridges running down its sides (usually five but can sometimes vary); in cross-section, it resembles a star, hence its name. The entire fruit is edible and is usually eaten out of hand. They may also be used in cooking and can be made into relishes, preserves, and juice drinks.

The fruit is about 5 to 15 centimetres (2 to 6 inches) in length and is an oval shape. It usually has five prominent longitudinal ridges, but in rare instances it can have as few as four or as many as eight. In cross section, it resembles a star. The skin is thin, smooth, and waxy and turns a light to dark yellow when ripe. The flesh is translucent and light yellow to yellow in color. Each fruit can have 10 to 12 flat light brown seeds about 6 to 13 mm (0.25 to 0.5 in) in width and enclosed in gelatinous aril. Once removed from the fruit, they lose viability within a few days.[2][3][4]

Like the closely related bilimbi, there are two main types of carambola: the small sour (or tart) type and the larger sweet type. The sour varieties have a higher oxalic acid content than the sweet type. A number of cultivars have been developed in recent years. The most common cultivars grown commercially include the sweet types "Arkin" (Florida), "Dah Pon" (Taiwan), "Ma fueng" (Thailand), "Maha" (Malaysia), and "Demak" (Indonesia) and the sour types "Golden Star", "Newcomb", "Star King", and "Thayer" (all from Florida). Some of the sour varieties like "Golden Star" can become sweet if allowed to ripen.[1][2][3]

The entire fruit is edible, including the slightly waxy skin. The flesh is crunchy, firm, and extremely juicy. It does not contain fibers and has a texture similar in consistency to that of grapes. Carambolas are best consumed shortly after they ripen, when they are yellow with a light shade of green or just after all traces of green have disappeared. They will also have brown ridges at the edges and feel firm. Fruits picked while still slightly green will turn yellow in storage at room temperature, but will not increase in sugar content. Overripe carambola will be yellow with brown spots and can become blander in taste and soggier in consistency.[3][5]

Ripe sweet type carambolas are sweet without being overwhelming as they rarely have more than 4% sugar content. They have a tart, sour undertone, and an oxalic acid odor. The taste is difficult to compare, but it has been likened to a mix of apple, pear, grape, and citrus family fruits. Unripe starfruits are firmer and sour, and taste like green apples.[2][6]

Ripe carambolas may also be used in cooking. In Southeast Asia, they are usually stewed in cloves and sugar, sometimes with apples. In China, they are cooked with fish. In Australia, they may be cooked as a vegetable, pickled, or made into jams. In Jamaica they are sometimes dried.[1]

Unripe and sour type carambolas can be mixed with other chopped spices to make relishes in Australia.[1] In the Philippines, unripe carambolas are eaten dipped in rock salt.[7] In Thailand, they are cooked together with shrimp.[1]

The juice from carambolas is also used in iced drinks, particularly the juice of the sour varieties. In Hawaii they are used to make sherbet, while in the Philippines they can be used as seasoning. In India, the juice is bottled for drinking.[1]

Carambola is rich in antioxidants, potassium, and vitamin C; and low in sugar, sodium, and acid. It is also a potent source of both primary and secondary polyphenolic antioxidants.[8]Averrhoa carambola has both antioxidant and antimicrobial activities. Scavenging of nitric oxide (NO) by the fruit extract is dependent on concentration and stage of ripening. Extracts showed antimicrobial activity against E. coli, Klebsiella spp., Staphylococcus aureus, and Pseudomonas aeruginosa.[9][10] In South Asian countries, there is a belief that eating Carambola fruit enhances the sex drive of males. Its name "Kamaranga - කාමරංගා", in Sinhala language (Sri Lanka) and kamranga (কামরাঙ্গা) in Bengali means it.

Carambolas contains caramboxin[11] and oxalic acid. Both substances are harmful to individuals suffering from kidney failure, kidney stones, or those under kidney dialysis treatment. Consumption by those with kidney failure can produce hiccups, vomiting, nausea, mental confusion, and sometimes death.[12][13][14][15][16][17] Recent research has identified caramboxin as a neurotoxin which is structurally similar to phenylalanine, and is a glutamatergic agonist.[11] Despite its toxicity to renally-compromised individuals, the levels of oxalic acid and caramboxin in starfruit are low enough to be safely processed by the general population, for whom it is both a safe and healthy food.

Like the grapefruit, carambola is considered to be a potent inhibitor of seven cytochrome P450 isoforms.[18][19] These enzymes are significant in the first-pass elimination of many medicines, and, thus, the consumption of carambola or its juice in combination with certain prescription medications can significantly increase their effective dosage within the body. Research into grapefruit juice (its potent enzymes) for instance, identified a significant effect (requires change in dose or other side effects) on common medications when taken concurrently by the patient, including statins, which are commonly used to treat high cholesterol and cardiovascular illness, opiates/opioids, and benzodiazepines (a sedative tranquilizer drug family that includes diazepam).[20][citation needed]

The carambola is a tropical and subtropical fruit which can be grown at elevations up to 1,200 metres (4,000 feet). It prefers full sun exposure, but requires enough humidity and annual rainfall of at least 1,800 mm (70 in). It does not have a soil type preference, but it requires good drainage.[citation needed]

Carambola trees are planted at least 6 m (20 ft) from each other and typically are fertilized three times a year. The tree grows rapidly and typically produces fruit at four or five years of age. The large amount of rain during spring actually reduces the amount of fruit, but, in ideal conditions, carambola can produce from 90 to 180 kilograms (200 to 400 pounds) of fruit a year. The carambola tree flowers throughout the year, with main fruiting seasons from April to June and October to December in Malaysia,[21] for example, but fruiting also occurs at other times in some other locales, such as South Florida.[3]

Major pests are fruit flies, fruit moths, ants, and birds.[2][21] Crops are also susceptible to frost.[2]

Top producers of carambola in the world market include Australia, Guyana, India, Israel, Malaysia, the Philippines, Taiwan, and the United States.[3] Malaysia is a global leader in starfruit production by volume and ships the product widely to Asia and Europe.[21] Due to concerns over pests and pathogens, however, whole starfruits cannot yet be imported to the US from Malaysia under current United States Department of Agriculture regulations. In the United States, carambolas are grown in tropical and semitropical areas, including Texas, Florida and Hawaii.[1][22]

In the United States, commercial cultivation and broad consumer acceptance of the fruit only dates to the 1970s. That acceptance is attributable to Morris Arkin, a backyard horticulturalist, from Coral Gables, Florida. During the late 1960s, Arkin began cultivating plants and trees in his backyard, eventually developing a kind of carambola, or star fruit, that became commercially viable and was named after him. Until the early 1970s, carambola had been grown only as specimen trees in botanical gardens and experiment stations and as a curiosity in home landscapes. However, because of its attractive star shape when cut in cross-section and yellow to golden color, it began to grow in popularity. Fruit from early introductions were however, sour and sometimes considered unpalatable. This limited market and public acceptance, inhibiting development and expansion of carambola as a commercial fresh fruit. Arkin cultivated the 'Arkin' variety – a sweet carambola with good handling characteristics – in the mid to late 1970s. Soon afterward, the limited commercial area of carambola under cultivation in south Florida (4 to 12 ha) was top-worked to 'Arkin' and this new cultivar led to a rapid increase in consumer demand for the fruit which further stimulated interest in establishing new commercial plantings. Today, the 'Arkin' variety represents 98% of the current acreage in South Florida.[23]

The trees are also grown as ornamentals for their abundant brightly colored and unusually shaped fruits, as well as for their attractive dark green leaves and their lavender to pink flowers.[3]

Like the bilimbi, the juice of the more acidic sour types can be used to clean rusty or tarnished metal (especially brass) as well as bleach rust stains from cloth. They may also be used as a mordant in dyeing.[1]

The Portuguese word carambola, first known use 1598, was taken from Marathi karambal derived from Sanskrit karmaphala.[24]

The carambola is known under different names in different countries. It should not be confused with the closely related bilimbi, with which it shares some common names. It is also called "starfruit" in English (including Jamaican English and Philippine English) and literally translates into Stjernefrugt in Danish, Sternfrucht in German, and Stjärnfrukt in Swedish. In Spanish, it is known as carambola, carambolo, tamarindo chino, tamarindo culí, balimbín (Philippine Spanish, from Tagalog balimbing, plural is balimbines), and fruta china (Ecuador).